The present invention relates to a power source apparatus for a car, and especially to a power source apparatus with different voltage levels.
The electrical power consumed in a car has increased from year to year. Accordingly, a method, corresponding with high-power-consuming components mounted in a car by situating a high-voltage battery besides a conventional low-voltage battery, is known.
For example, a method of charging a 14V low-voltage battery and a 42V high-voltage battery in a car is disclosed in a paper titled xe2x80x9cConsideration Implementing a Dual Voltage Power Networkxe2x80x9d by S. Muller and X. Pfab, Proc. of Convergence 98, Detroit, U. S. A., 1998. In this method, two kinds of batteries are charged by converting alternating current (AC) power generated by an alternator to direct current (DC) power, and feeding the DC power while switching two switches. According to this method, since it is possible to charge two batteries without using a DC/DC converter, a charging system can be constructed at a low price.
However, if an anomaly occurs in a battery controller for controlling the two switches, and the two switches cannot be turned on, it becomes impossible to charge the two batteries, with the power generated by a motor in a car. Consequently, when the charged power is consumed by the running of the car, the car will stop.
An object of the present invention is to provide a power source apparatus which makes it possible to run a vehicle without stopping the vehicle even if a battery controller breaks down.
Also, another object of the present invention is to provide a power source apparatus which makes it possible to start an engine of a vehicle even if the engine is in a stop state when the battery controller breaks down.
To achieve the above objectives, the present invention provides a power source apparatus for a car, comprising: a high-voltage battery and a low-voltage battery; an inverter for performing power-conversion of the voltage from one of the two batteries; a first switching element for controlling power-feed in the direction from the high-voltage battery to the inverter; and a second switching element for controlling power-feed in the direction from the inverter to the low-voltage battery.
In the above power source apparatus, six switching elements which compose the inverter are integrated with the first and second switching elements.
Further, in the above power source apparatus, one terminal of the first switching element and one terminal of the second switching element are connected to positive pole terminals of the high-voltage and low-voltage batteries, respectively; and the other terminal of the first switching element and the other terminal of the second switching element are connected to a positive pole terminal at the direct current side of the inverter.
Furthermore, in the above power source apparatus, wherein the first switching element is composed of a first field effect transistor (FET) and a diode connected to the first FET in the reverse direction; the second switching element is composed of a second FET and a diode connected to the second FET in the forward direction; and when current flows from a source to a drain of one of the first and second switching elements, the current is controlled so as to flow in one of the first switching element and the second switching element by turning on a gate of this switching element.
Also, in the above power source apparatus, the output voltage of the inverter is controlled corresponding with states of the first and second switching elements.
Moreover, in the above power source apparatus, the inverter is connected to a motor; and if at least one of the first and second switching elements becomes uncontrollable, the output voltage of the inverter is controlled by determining in which of a driving state and a generating state the motor is operated.
That is, in the above power source apparatus, even if a battery controller for controlling the first and second switching elements breaks down, by controlling the output voltage at the direct current side of the inverter so as to be higher than that of the high-voltage battery, the high-voltage battery can be charged with power generated by the motor via the diode connected to the first FET of the first switching element, in the reverse direction. Thus, by feeding power to the high-power electrical loads necessary for the running of the car from the high-voltage battery, it is possible to drive the car until the fuel for the engine is completely consumed.
Further, if the engine is stopped, only by controlling the inverter, it is possible to convert direct-current power fed from the low-voltage battery via the diode connected to the second switching element. Accordingly, the motor can be driven, which in turn can start the engine. Thus, even if the first and second switching elements are uncontrollable, the car can be started.